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Multilevel Queue Scheduling in Operating System
Operating systems use a particular kind of scheduling algorithm called multilevel queue scheduling to control how resources are distributed across distinct tasks. It is an adaptation of the conventional queue-based scheduling method, in which processes are grouped according to their priority, process type, or other factors
The system can allocate system resources based on the priority and needs of the processes by assigning a separate scheduling algorithm to each queue. For instance, the background queue may employ first-come-first-serve scheduling to maximize the usage of system resources for longer-running activities, while the foreground queue might use Round Robin scheduling to prioritize interactive processes and speed up reaction time.
The goal of multilevel queue scheduling is to strike a compromise between fairness and performance. The system can increase overall performance while making sure that all processes are treated equitably by giving some processes more priority than others and distributing resources accordingly
Components of the MLQ architecture
In an MLQ (Multilevel Queue) architecture, the system is divided into multiple queues or levels based on the type of processes. The MLQ architecture aims to efficiently handle different types of processes and prioritize their execution based on their characteristics.
The main components of an MLQ architecture are
System Processes − System processes refer to operating system tasks or processes that are essential for the proper functioning of the system. These processes handle critical operations such as memory management, process scheduling, I/O handling, and other system-level functions. System processes typically have the highest priority in the MLQ architecture and are executed before other types of processes.
Interactive Processes − Interactive processes are user-oriented processes that require an immediate or near-real-time response. These processes are typically initiated by user interaction, such as keyboard input or mouse clicks. Examples of interactive processes include running a text editor, web browser, or a graphical application. Interactive processes are given priority in the MLQ architecture to ensure a smooth and responsive user experience.
Batch Processes − Batch processes are non-interactive processes that are executed in the background without direct user interaction. These processes often involve executing a series of tasks or jobs that can be automated and executed without user intervention. Batch processes are typically resource-intensive and can include tasks such as data processing, large-scale computations, or scheduled backups. In the MLQ architecture, batch processes are allocated resources based on their priority, but they are generally given lower priority compared to interactive processes.
Different Levels of Queues
Processes are divided into many tiers of queues in multilevel queue scheduling according to their features, priority, and time limitations. The following various layers of queues can be utilized in multilevel queue scheduling:
Foreground Queue − Interactive processes that demand quick system responses often use this queue. Usually, these procedures receive first attention
Background Queue − This queue is used for non-interactive processes that take longer to complete. These tasks are prioritized less than foreground tasks.
Interactive queue − The interactive queue is used for processes that demand a system response in a reasonable amount of time
Batch Queue − This queue is used for batch processing, or processing many jobs at once. These tasks typically call for lengthy execution times and are submitted in advance.
System Queue − This queue is used for system processes, such as device drivers and interrupt handlers, that need special permissions to complete their tasks. Usually, these procedures receive first attention.
Real-time Queue − Real-time processes, which demand a prompt response from the system, are queued in this way. Usually, these procedures receive first attention.
Implementation of Multilevel Queue Scheduling
When using multilevel queue scheduling, the processes are split up into different queues according to their characteristics and priority, and then they are scheduled using the scheduling algorithm for each queue. The following steps are needed to implement multilevel queue scheduling −
Sort the processes into several tiers of queues according to their attributes, such as priority, deadlines, and I/O demands.
Choose the optimal scheduling algorithm for each queue based on the kinds of processes it contains. For instance, the batch queue might employ a First-Come-First- Serve (FCFS) scheduling strategy whereas the foreground queue might use a round robin scheduling algorithm.
Give each queue a priority based on how important the processes in it are. For instance, the batch queue might have the lowest priority while the foreground queue might have the greatest priority
A process is positioned in the proper queue when it enters the system based on its characteristics. An interactive process, for instance, could go in the interactive queue, whereas a batch job could go in the batch queue.
Using the appropriate scheduling method for that queue, the scheduler chooses a process from the top of the queue that has a process scheduled to be executed and prepares it for execution
The scheduler chooses the next process to be executed from the highest priority queue that contains a process waiting to be executed whenever the process has finished its execution or is blocked on I/O.
The procedure keeps going until every process in the system has finished running.
Advantages
Multilevel queue scheduling benefits include
Based on the characteristics of the processes, multilevel queue scheduling enables the operating system to distribute resources efficiently. As a result, the system's overall reaction time is decreased through effective resource utilization.
The system responds quickly to operations with a higher priority, such as interactive processes, thanks to multilevel queue scheduling. This makes the system more responsive overall, which enhances the user experience.
The operating system can prioritize operations according to their relevance via multilevel queue scheduling, ensuring that crucial tasks are carried out first.
Multilevel queue scheduling can boost system throughput and performance concurrently scheduling tasks from various queues.
Disadvantages
Multilevel Queue Scheduling Drawbacks
A careful choice of scheduling algorithms and priorities for each queue is necessary when using the complex scheduling method known as multilevel queue scheduling. It may be challenging to design and execute, and implementation mistakes may result in system instability and subpar performance.
The system's complexity may increase and its performance may be adversely affected by the usage of various queues and scheduling algorithms.
A process may experience starvation if it is assigned to a lower-priority queue and never has the chance to run, especially if higher-priority processes continually enter the system.
Multiple queues can occasionally lead to inefficient resource use, especially if they are not properly designed and managed
Conclusion
Operating systems employ the potent scheduling technique known as multilevel queue scheduling to manage several queues of processes with various requirements and features. Multilevel queue scheduling can improve system performance by categorizing processes into various queues according to their characteristics, such as priority, execution time, and resource requirements.
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